1. Field of the Invention
This invention relates generally to a device for cryogenic cooling. More particularly, the present invention relates to a cryogenic refrigerator which utilizes a displacer to optimize heat exchanger performance and reduce dead space, separates the displacement and compression functions, and eliminates unwanted vibration. More specifically, the present invention relates to a Stirling-Cycle refrigerator which utilizes a ferroelectrically actuated diaphragm compressor pump, a ferroelectrically actuated diaphragm expander pump and a ferroelectrically actuated diaphragm displacer pump, wherein each pump has one or more high displacement ferroelectric actuators.
2. Description of the Related Art
Problems existing with present Stirling cycle cryogenic refrigerators include deleterious effects of dead space, lack of controllability of flow rate, contamination of the working fluid, and unwanted vibration. The mechanical vibrations are transmitted to the sensitive, delicate optical components being refrigerated. Also, cryocoolers have micro-sized fluid passages that are extremely sensitive to contamination. Piston devices use lubricants and/or produce wear particles which have a propensity to contaminate the area containing the working gas. Some devices also contain piston-to-cylinder clearance seals which are very complex. The need for highly precise manufacturing and assembly of the multitude of parts required for existing Stirling-cycle devices makes them costly.
An acoustic cryocooler having no moving parts is disclosed in U.S. Pat. No. 4,953,366. Pulse tubes replace the compressor and expander to generate a standing wave which drives the cryocooler. The resonator tubes have to be of sufficient length to support the resonant frequency of the standing wave; therefore, the cooler tends to be relatively large. Also, the frequency of the required standing wave is normally in the acoustic range which tends to make the units noisy. It would be advantageous to have a cryocooler which is more compact in size and which could be dynamically balanced to alleviate undesirable vibration and noise. It would also be advantageous to have a Stirling-cycle cryocooler which avoids contamination. Lastly, a design which removes the deleterious effects of dead space and allows for control of flow rate through the heat exchangers would be beneficial.